Atomic Structure Timeline

Welcome to the atomic structure timeline. This site explores discoveries related to atomic structure including the electron, proton and neutron. The dates used for events are open to debate since many scientist's spent decades studying a topic. Check the links for more in depth material. Most of all enjoy.

Early theories of the structure of matter were not based upon experiments. As scientists began to study the relationship between several physical phenomenon such as electricity, and magnetism they began to develop different models about atomic structure.

Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.

1886

E. Goldstein

Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.

Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay.

Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.

Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

1919

Aston

Discovered the existence of isotopes through the use of a mass spectrograph.